Question
Asked Nov 26, 2019
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When 271. mg of a certain molecular compound X are dissolved in 25.0g of benzene C6H6, the freezing point of the solution is measured to be 0.5°C. Calculate the molar mass of X.

 

If you need any additional information on benzene, use only what you find in the ALEKS Data resource. Also, be sure your answer has a unit symbol, and is rounded to 2 significant digits.

molal freezing point depression constant (Kf)
°C·kg·mol−1  of benzene is 5.07

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Expert Answer

Step 1

Given:

Mass of molecular compound X=271. mg

Mass of benzene=25.0 g

Freezing point of solution=0.5oC

Molal freezing point depression constant(Kf) of benzene=5.07 OC .Kg.mol-1

Conversion:

From mg to g:

Mass of molecular compound X=271. mg

                                                                      =271/1000=0.271 g

From g to Kg:

Mass of benzene=25.0 g

                                     =25.0/1000=0.025 Kg

Step 2

To calculate molar mass of X(solute):

First we have to find molality, the following equation is

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AT-T-T;iKm where T, and T, are freezing points of solution and pure solvent(benzene) i is the van't Hoff factor. Fornon-electrolytesi=1 Kmolalfreezing point depression constant of benzene mols solute mismolality of solution.i.e Kgsolvent

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Step 3

Substitute all the values in the above equation, we get the molal...

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Image Transcriptionclose

AT=T,-T iKm AT-0.5°C-5.53°C(1(5.07°C.Kg.mol" )(m) 0.9921mols solute m- Kg solvent

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